From its landing site near Mars's north pole, the lander has collected and analyzed soil samples that show minerals on Mars that are associated with liquid water on Earth.

Phoenix also recorded the planet's real-time transition from summer to fall, which revealed tantalizing evidence of an ongoing hydrological cycle, said Peter Smith, Phoenix's principal investigator based at the University of Arizona.

Jim Whiteway, lead scientist for the Phoenix Meteorological Station, said that instruments on board the craft recorded rising temperatures and humidity in the two months leading up to the Martian summer solstice in July.

Temperatures have been falling ever since.

"In the second half of the mission we saw frost, ground fog, and clouds. This is now occurring every night," Whiteway said.

Ice crystals were detected coming from clouds about 2.5 miles (4 kilometers) above the spacecraft's landing site. The crystals are most likely water-based, the scientists said, because it's not yet cold enough on Mars for carbon-dioxide snow to form.

The team hopes Phoenix will help confirm whether the snow hits the ground before the craft—which has already survived beyond its expected lifespan—freezes up forever during the cold Martian winter.

"We're going to be watching very closely for the next months to see if the snow is falling on the Martian surface," Whiteway said.

Rewriting Mars's Geochemistry

The latest soil data from Phoenix have confirmed the presence of calcium carbonates, common clays found in wet environments on Earth.